Losing hope...

My fiance and I want a baby more than anything. Watching people like my ungrateful sister accidentally haveing 5 children that she doesn't take care of while I've been struggling for over a year to get pregnant is draining me of hope. I got pregnant on our first try and lost my baby at 6 weeks and since then we haven't been able to conceive, doctors say there's nothing wrong, timing is everything, were healthy and young. But every time I get my period I fall into this sink hole, thinking im not trying hard enough, maybe it's the coffee, maybe I need to work out more, I'm just stressing too much and ive made my body not ready for a child but the want for a child is so intense. I want a family. I'm just feeling down.